This invention relates to an apparatus used to maintain a specimen at a low temperature for a long period of time and, more particularly, to a cold reserving apparatus used for refrigeration storage of livestock spermatozoa, measurement of critical temperatures of superconductors, storage of liquid nitrogen, and so forth.
A method of freezing spermatozoa in a suitable vessel by liquid nitrogen is known as one of simplest methods of refrigeration storage of spermatozoa factitiously taken from a livestock such as a bull. To lengthen the term of refrigeration storage based on this method, it is necessary to perform troublesome operations of periodically replenishing liquid nitrogen to maitain a desired low temperature. In the field of superconducting material, it is indispensable to measure the critical temperature of a newly developed superconducting material. One example of generally used conventional apparatus for measuring critical temperatures has a construction in which a specimen accommodation chamber is disposed in an adiabatic vacuum in a position adjacent to a cooling stage of a Gifford-McMahon refrigerator or an improved type thereof. In another example, a refrigeration chamber in which liquid nitrogen or liquid helium is contained and a specimen accommodation chamber disposed under the refrigeration chamber adjacently thereto are provided in a vacuum vessel. In both these temperature test apparatus, the capacity of the specimen accommodation chamber cannot be increased beyond a limit which is determined in relation to the size of the refrigerator or refrigerant container adjacent to the specimen accommodation chamber. In addition, the adiabatic vacuum is necessarily lost each time a specimen is replaced. At the same time, the operation of the refrigerator must be stopped in the case of the former type of apparatus. Therefore, a low-temperature atmosphere in a specimen chamber formed in the process of the preceding test cannot be maintained and used for the succeeding test, as the temperature of the specimen chamber is returned to the room temperature at the time of replacement of a specimen.